As conventional methods for producing positively chargeable toner, dry methods such as a pulverizing method, or wet methods such as a phase inversion emulsification method are known.
In the pulverizing method, a charge-controlling agent is added to a binder resin and the resulting mixture is then melt-kneaded. Therefore, a major portion of the charge-controlling agent becomes embedded in the inner portion of a particle, so that only a portion of the charge-controlling agent is exposed to the surface of the particle, thereby contributing to impart charge.
For this reason, the pulverizing method is disadvantageously less effective in imparting charge with respect to the amount of the charge-controlling agent added.
In the phase inversion emulsification method, for example, toner particles are produced by neutralizing a binder resin having a tertiary amino group to improve hydrophilicity, and emulsifying the binder resin through phase inversion in a water medium.
However, this method inevitably generates odor originating from the amino group. Further, when a charge-controlling agent is added before phase inversion, and the resulting mixture is then emulsified through phase inversion, the same disadvantage exists that a major portion of the charge-controlling agent becomes embedded in the inner portion of a particle, so that only a portion of the charge-controlling agent is exposed to the surface of the particle. In addition, when an ionic group such as a tertiary amino group is contained, there is a disadvantage that particles are poorly formed during phase-inversion emulsification.
To cope with these disadvantages, there has been proposed a method for producing a toner in the following procedure. For example, a mixture of a basic group-containing resin which becomes self-dispersible and/or soluble in water through neutralization and a positively chargeable charge-controlling agent as essential components are emulsified through phase inversion into a water medium under the presence of a neutralizing agent, to thereby prepare an aqueous dispersion and/or aqueous solution of fine particles. Then, the aqueous dispersion and/or aqueous solution of the fine particles are mixed with an aqueous dispersion of toner particles having a colorant and a binder resin as essential components, and the basic group-containing resin containing a positively-chargeable controlling agent is deposited on the surfaces of the toner particles using a neutralizing agent having a polarity opposite to that of the aforementioned neutralizing agent. By doing this, the basic group-containing resin containing the positively-chargeable controlling agent is fixed on the surfaces of the toner particles, to thereby produce a toner.
There has been proposed another method for producing a spherical toner having positively-charging characteristics in the following procedure. For example, an aqueous dispersion of resin particles having a binder resin and a colorant as essential components, and a separately-prepared aqueous dispersion of basic group-containing resin microparticles having carbon black as an essential component are mixed to thereby deposit fine particles on the surfaces of the resin particles. After drying of the resin particles, the particles are mixed with stirring to make the surfaces of the toner particles stable and uniform, and negative-charging, inorganic microparticles are externally added to the toner particles, whereby a spherical toner is produced.